Bioluminescence is a non-invasive technique for performing in vivo diagnostic studies on animal subjects in the areas of medical research, pathology and drug discovery and development. Bioluminescence is typically produced by cells that have been transfected with a luminescent reporter such as luciferase and can be used as a marker to differentiate a specific tissue type (e.g. a tumor), monitor physiological function, track the distribution of a therapeutic compound administered to the subject, or the progression of a disease. A wide range of applications have been demonstrated including areas of oncology, infectious disease, and transgenic animals.
Photons emitted by bioluminescent cells are strongly scattered in the tissue of the subject such that propagation is diffusive in nature. As photons diffuse through tissue many are absorbed, but a fraction reach the surface of the subject and can be detected. In general, absorption in mammalian tissues is high in the blue-green part of the spectrum (<600 nm) and low in the red and NIR part of the spectrum (600-900 nm). Firefly luciferase has a rather broad emission spectrum ranging from 500-700 nm, so at least part of the emission is in the low absorption region. Since the mean-free-path for scattering in tissue is short, on the order of ˜0.5 mm, photons from deep sources are scattered many times before reaching the surface.
One bioluminescent application is referred to as bioluminescent imaging. Such bioluminescent imaging systems effectively record the spatial distribution of these photons emitted from the surface of the subject. Some specialized in-vivo imaging applications may include analysis of one or more representations of emissions from internal portions of a specimen superimposed on a photographic representation of the specimen. The photographic representation provides the user with a pictorial reference of the specimen. The luminescence representation indicates portions of the specimen where an activity of interest may be taking place.
Obtaining the luminescence representation may involve image capture over an extended period of time, e.g., minutes. The living specimen is typically anesthetized during this time to prevent movement that may compromise image capture. Accordingly, these imaging systems require complex anesthesia delivery systems to deliver anesthesia gases to the specimen. Additionally, such luminescence imaging systems tend to be expensive and difficult to maintain. All these factors result in low throughput for analyzing specimens.
Hence, there is interest in developing both improved luminescence detection systems that would provide simple and efficient low cost systems, which do not require anesthesia for the specimen.